The present invention generally relates to video signal recording apparatuses, and more particularly to a video signal recording apparatus which employs a system for recording a main video signal part of a composite video signal onto a magnetic tape by a main head and records a signal part including other signals such as a vertical synchronizing signal onto the magnetic tape by a sub-head, in which the recording is carried out so that reproduction can also be carried out by a standardized apparatus of a standard type wherein the reproduction is carried out alternately by two main heads.
Presently, video signal recording and/or reproducing apparatuses using tape cassettes are reduced to practical use on a world-wide basis. As types of these recording and/or reproducing apparatuses using tape cassettes, standardized apparatuses of two or three standard types presently exist world-widely. There is no interchangeability among apparatuses of different standards, however, interchangeability exists among apparatuses adopting the same standard. Accordingly, a tape cassette recorded by one recording and/or reproducing apparatus can be reproduced by another recording and/or reproducing apparatus of the same standard. Hence, in order to ensure interchangeability among different recording and/or reproducing apparatuses manufactured by different manufacturers so as to carry out recording and/or reproduction, a standardization is set with respect to formats of the tape cassette and the recording and/or reproducing apparatus. That is, the above formats are standardized for each standard, and a standard type tape cassette and a standard type recording and/or reproducing apparatus are respectively provided and employed for each standard.
In the above standard type recording and/or reproducing apparatus, a magnetic tape is caused to travel in a state where the magnetic tape is wrapped obliquely around a guide drum making contact with the guide drum for an angular range slightly larger than 180.degree.. Two rotary heads are provided at mutually diametrical positions of a rotary body such as a rotary drum or a rotary head bar, and a so-called two-head system is employed wherein a video signal is recorded onto and reproduced from tracks formed obliquely with respect to the longitudinal direction of the magnetic tape by the two rotary heads.
Among the standard type apparatuses, a typical standard apparatus proposed by the present assignee is widely used. In this typical standard type apparatus, the two rotary heads are so-called azimuth heads having mutually opposite azimuth angles, and the tracks formed by these heads are in contiguous contact without guard bands formed therebetween. Further, a standardization is set with respect to the tape width, track inclination, track width (track pitch), diameter of the guide drum (cylinder), and the like.
Recently, a problem of much importance involves the realization in downsizing the recording and/or reproducing apparatus main body. This is to realize a more compact portable type recording and/or reproducing apparatus, and, for example, to realize such an equipment that a recording apparatus is unitarily built into a television camera. In order to downsize the apparatus main body, it becomes necessary to downsize the guide drum which occupies a large part within the apparatus. If the diameter of the guide drum can be set small, the area occupied by the guide drum can be reduced, and further, a mechanism for drawing out the tape from the tape cassette and causing the tape to make contact with the guide drum can be designed as a small mechanism.
However, in the above two-head system, the tape pattern will change if the diameter of the guide drum is reduced, and the interchangeability cannot be obtained. In addition, the scanning length (track length) of each head over the magnetic tape becomes shorter. As a result, unless the precondition for recording one field of video signal on one track is changed, the relative speed of the head with respect to the tape becomes reduced, the signal-to-noise ratio is greatly reduced, and it becomes impossible to carry out satisfactory recording and reproduction. Accordingly, it is in reality impossible to reduce the diameter of the guide drum in the apparatus of the two-head system.
In this regard, some attempts have been made to realize a compact type recording and/or reproducing apparatus which uses a tape pattern and format completely different from those of the standard type recording and/or reproducing apparatus. In one of such attempts, the apparatus only uses a single rotary head, and the magnetic tape is caused to travel in a state where the tape is wrapped around the guide drum for an angular range of 360.degree.. In this so-called one-head system, it becomes possible to reduce the diameter of the guide drum to one-half that of the above apparatus of the two-head system. However, dropout is introduced in the recorded video signal when the single head scans over the tape wrapped around the guide drum exceeding one side edge and the other side edge of the tape. Particularly if tracks for a control signal and an audio signal are formed at the side edges of the tape, there was a disadvantage in that dropout is introduced in the video signal at these parts. Moreover, because only a single head is used, a so-called overlap recording in which the same signal is recorded overlapping at a terminal end of one track and a starting end of an adjacent track cannot be carried out in essence. Hence, also from this point of view, there was a disadvantage in that a continuous reproduced signal having no dropout cannot be obtained upon reproduction. Therefore, this apparatus of the one-head system was never developed to a stage for reduction into practical use.
An apparatus of the so-called 1.5-head system was thus proposed as a system eliminating the disadvantages of the above one-head system. In the apparatus of the 1.5-head system, the magnetic tape is wrapped around the guide drum for an angular range slightly smaller than 360.degree.. A large portion of the video signal within the composite video signal is recorded onto the tape by a main head, and a sub-head records the remaining signal portion including the vertical synchronizing signal onto the tape during a period in which the main head does not make contact with the tape.
According to the above apparatus of the 1.5-head system, the diameter of the guide drum can be made to one-half that of the two-head system, as in the case of the one-head system, to enable downsizing of the apparatus. Furthermore, the 1.5-head system was advantageous in that the recording and reproduction can be carried out without introducing dropout in the signal. However, the format of the tape pattern and the like of the conventional 1.5-head system completely differs from the format of the standard type apparatus of the standardized two-head system described previously. For example, in the standard type apparatus of the two-head system, azimuth heads are used to form tracks in contiguous contact with each other. On the other hand, in the apparatus of the 1.5-head system, azimuth heads are not used, and the tracks are formed with unrecorded guard bands formed therebetween. For this reason, there was a disadvantage in that the magnetic tape recorded by the apparatus of the 1.5-head system cannot be reproduced by the standard type apparatus of the two-head system.